The size of the memory is not playing seems to be no difference between
You need to set HashCnt > 512 to see the difference, but you cannot do it because of 1GB. Therefore, no speedup for 1GB cards.
I tried to 2Gb cards all possible values of the parameter h. And compared with 1Gb cards only in the negative (or 0 difference)
I don't have such cards here so I cannot investigate it deeply, but if you have 2GB and it does not help - it means that card cannot use entire memory bandwith, too few computing units for that. If so, it's useless to use "-h" parameter, miner will select optimal value automatically.